Arrangement for reducing temperature stresses in the end and corner portions of castings



Dec. 16, 1941. H. HOLZWARTH 6, 0

ARRANGEMENT FOR REDUCING TEMPERATURE STRESSES IN THE END AND CORNER PORTIONS 0F CASTINGS Filed June 29, 1939 2 Sheets-Sheet l INVENTOR I'M/V6 HOLZWAR TH W +W ATTORNEYS H; REDUCING TEMPERATU Dec. 16, 1941. HQLZWARTH 2,266,600

ARRANGEMENT FOR RE STRESSES IN THE END AND CORNER PORTIONS OF CASTINGS Filed June 29, 1939 2 Sheets-Sheet 2 INVENTOR HANS HOLZWART/r' ATTORNEYS occur at such edges and corners.

Patented Dec. 16, 1941 ARRANGEMENT FOR REDUCING TEMZPERA- TURE STRESSES IN THE END AND CORNER PORTIONS OF CASTINGS Hans Holzwarth, Dusseldorf, Germany, assignor to Holzwarth Gas Turbine 00., San Francisco, Calif., a corporation of Delaware Application June 29, 1939, Serial No. 281,850

Germany June 30, 1938 8 Claims.

The present invention relates to the construction of highly heated parts of combustion engines and other heat apparatus, and more particularly to th construction of castings which in use are subjected not only to high temperatures but also to high pressure..

It is the general object of the invention to provide an arrangement and construction for highly heated engine and other castings whereby heat strains and also stresses resulting from temperature differences in the end and corner pieces of such castings, and particularly of combustion turbine parts having hollow interiors, are reduced.

It has been found in practice that if the edge or corner pieces of heavy engine castings are formed in th usual way, then two simultaneously occurring circumstances operate together to cause the heat and temperature stresses to rise to a particularly high degree at the edges or corners. First of all, the manufacture of the edges or corners as an integral partof a casting unavoidably brings with it the result that thickening of the walls and thus accumulations of material Anatural limit is set to attempts to eliminate these thickenings of walls in view of possible core diaplacements, so that the generally unavoidable accumulation of material increases the stresses which must appear by reason of the heat flow through the walls and the resulting temperature drop through the large mass of material. n the other hand, such highly stressed edge and corner parts, when the associated machine parts serve for conducting highly heated media, like superheated steam. combustion gases, etc., occur frequently where these media assume particularly high velocities. This is especially true in combustion gas turbines, and particularly in explosion turbines, as such edges are arranged therein at the seating surfaces of valves, at the joints between individual combustion chamber parts, at the points of attachment of nozzles, etc.

It is in general known that the heat transfer between the heat transferring medium and heat receiving wall increases strongly with increase of the velocity'of th medium, the increase being very sudden when the flow velocity reaches the neighborhood of the velocity of sound. Under the influence of increased heat transfers which thus come into action at points of thick accumulations of material, the edges and corners are exposed to excessive stresses so that after a comparatively short time injury to the edges and corners, above all the formation of fissures and cracks, can be found in an otherwise entirely undamaged casting. As a result, not only can the cooling agent escape in the case of cooled machine parts, but the hot gases on their side can penetrate into the cooling spaces, and in view of their generally higher pressures they force back the cooling agent and so can give rise to complete destruction of the casting.

According to the present invention, the edges and corners of castings are made of separate pieces and are so formed and constructed that accumulations of material and excessive thickenings of the wall are completely avoided; in fact. the wall thicknessis reduced at the actual corners or edges, the thickness increasing toward the areas of juncture with the casting. This separate construction of the edge and corner portions makes it possible to form them of particularly suitable and reliable building material for taking up safely the increased heat and temperature stresses which unavoidably result from the high velocity of the heat transferring medium at the edges and corners.

The edge or corner pieces are accordingly made of special inserts arranged in the casting and rigidly connected therewith, advantageously following the shape of the casting, and having at least at the actual edges or corners a reduced wall thickness compared to the casting, the'thickness increasing from the region of highest stress 'toward the points of connection with the casting. In a further development of the inventive idea, the hollow spaces resulting from the reduction of the wall thickness of the inserts in the casting are shaped as cooling spaces, being joined to form such cooling spaces particularly with the cooling spaces already present in the casting. The inserts are advantageously constructed as annular, angular pieces, that is, of open crosssection; they may be united with-the casting by welding. Ii th angle pieces have legs approximately perpendicular to each other or'if their cross-section is U-shaped, there results a particularly resilient construction which has the advantage of taking into account the difierent degrees of expansion which the individual walls of such castings experience in relation to each other.

The invention 'will be better understood by reference to the accompanying drawings wherein the invention is illustrated by way of example as embodied in a combustion engine plant. m said drawings:

Fig. 1 shows a longitudinal section through the controlled outlet valve of an explosion chamber 5 through whichthe combustion gases, after the explosion is complete, are discharged to the nozzles of a combustion turbine. Fig. 2, on the other hand, shows in longitudinal section a modified construction of theedge or corner insert of a combustion engine part in the form in which it may find application in the transition between the cylindrical and the conical part of a combustion chamber or at the transition between a valve housing and the machine part carrying the same. Fig. 3 shows a schematic view, partly in section, of an explosion turbine plant wherein are embodied the constructions of Figs. 1 and 2.

In Fig. 1, the numeral l represents a casting constructed as usual with double walls, the casting thus including a cooling space 2. The valve itself is designated by the reference character 3 and the valve stem is shown at 4. The valve stem is under the influenc of a controlmechanism (not shown) by which, aided by the explosion pressure which the combustion gases have assumed upon completion of the combustion, the valv 3 is lifted from its annular seat 5, whereupon thecombustion gases flow past the edge piece 5 first with super-critical velocity at the initially narrow outlet cross-section, and later with gradually falling velocity.

If the whole valve housing, including the valve seat 5, were constructed as an integral casting, the edge piece 5 would be subjected to extraordinarily high heat and. temperature stresses'to which it would not be equal in continuous operation. For it is evident, first of all, that the formation of the valve seat 5 as an integral part of the casting I would lead under all circumstances to an accumulation of material. Even when, during the finishing, account is taken of this fact from the beginning, the accumulation of material cannot be avoided because the thickening which is to be provided for forming the valve seat is again too small to be equalized by suitable shaping of the inner limiting surfaces of the casting. The position of the core could not in every case be so exactly determined and maintained during the pouring as to make it practical to attempt to equalize the thicknessrin this way. This very unavoidable accumulation of material would, however, in consequence of the extremely high heat transmissions occurring upon opening of the valve, and which must occur upon impingement of the seat by the combustion gases flowing at their maximum velocity and under their maximum pressure and temperature, cause such high temperature stresses that the seat would be unable to withstand them continuously.

The danger of cracking and bursting of the casting which results from the foregoing, at and in the vicinity of th valve seat, is eliminated in accordance with the invention by the fact that the edge piece 5 consists of a separate insert 8 arranged in the casting l and rigidly united therewith by the welding seams 6 and 1 or otherwise, the insert following at 8' the given shape of the casting I. This insert is of relatively small size and is given a greatly reduced wall thickness 9, especially at the edges or corners, in com- -paris on with the casting. Thus all material accumulations are, first of all, eliminated in the region of increased combustion gas velocities; in their place there are present rather unusually thin walls which are exposed to no considerable temperature differences between opposite surfaces thereof, and are therefore entirely relieved of dangerous temperatures stresses. The annular member 8, which is of U-shape in, cross-section,

can be separately manufactured, machined and inspected, thereby affording the possibility of selecting for the insert that material which, without regard to castability and the peculiarities conditioned by manufacture as a casting, best satisfies the existing requirements. Finally, the cores, which serve in the manufacture of the cooling chamber 2 in the casting I, can be secured and supported in an especially simple manner. The removal of the'core material itself after the casting is also facilitated so that the arrangement of the heretofore necessary picks serving for this purpose becomes superfluous.

It has already been mentioned that the insert 8 possesses a U-shaped cross-section. The hollow space HI created thereby is naturally constructed likewise as a cooling chamber in view of the arrangement of the cooling chamber 2 in the casting I and is accordingly joined directly with the cooling space 2 or united therewith. If the casting I has no cooling space, the produced hollow space ID will remain as such. It will then have the advantage of forming an air insulation which reduces or practically eliminates the heat transfer from the part 8 into the part I which, in view of the fact that the part 8 can be made of special heat-resistant material, may be less adapted than the part 8 for taking up large quantities of heat. It is within the scope of the invention to employ the so produced hollow space likewise as a cooling space when a necessity therefor arises.

Fig. 1 shows finally that all the walls of the insert member 8 have a thickness which is smaller than the wall thickness of the casting I, so that all stresses which could arise by reason of temperature diiferences are reduced to a degree which is tolerable in continuous operation.

The arrangement proposed in accordance with the invention for the nozzle valve of explosion chambers according to Fig. 1, has found in Fig. 2 an advantageous use at'the juncture of a casting I! provided with a cooling space H with another machine part. The casting [2 can, in such case, be the cylindrical middle section of an explosion chamber to which the conical inlet and outlet end sections are joined. It can equally well represent the housing of a valve which is fixed to another machine part. Also, the cooling chambers H can be formed in the most various ways. There is ail'ordedfirst the possibility of construction with annular cross-section. The cooling chambers l I can, however, be constructed als oas cylindrical bores in the casting l2 and can be arranged next to each other upon a circular arc, such construction being of particular advantage in explosion chambers. Independently of these constructional possibilities the construction, in accordance with the invention, is characterized as follows:

The edge piece of the casting consists of a separate insert l5 connected with the casting by way of the welding joints I 3, II. This insert, following at IS the given shape of the casting l2, has a considerably reduced wall thickness compared to the casting. The two legs of the annular angl piece stand approximately perpendicularly to each other, so that an extremely flexible edge closure for the casting I2 is obtained, which takes into account the different heat expansions of the outer and inner walls of the casting. By the reduction of. the wall thickness of the insert, in comparison with the wall thickness of the casting, and by the arrangement of the whole insert, there is created a hollow space I 6 which is connected with the cooling chamber ll of the casting into a common cooling chamber. The cooling agent can thus very easily reach the highly heated and therefore particularly thin edge I! of the insert l5, so that the heat withdrawal at this edge is reliably provided for. The temperature stresses, in spite of the comparatively high heat transmission which can occur at the edges I1, accordingly are maintained within the safe limits to be kept in continuous operation, so that the-danger f fissure and crack formation in the edge piece I is eliminated since at the point at which heretofore an accumulation of material was unavoidable, a great reduction in wall thickness has .occurred. As explained in connection with Fig. 1,

a series of further advantages with respect to the possibility ofchoice of suitable material and the carrying out of the finishing occurs by reason of the separate construction of the corner part.

The two constructions shown in Figs. 1 and 2 may be incorporated, as already indicated, in an explosion turbine plant. Such a plant is shown by way of example in Fig. 3, wherein the parts similar to those shown in Figs. 1 and 2 are similarly designated. As above explained, the region of highest heat and pressure stresses normally occur at the seat 8 of the outlet or nozzle valve 3, and in accordance with the invention, this seat is formed as an annular insert whose interior communicates with the hollow interior of the casting l to form a cooling chamber which receives a cooling agent such as water, which is fed by the pipe l8 leading from a pump l9 driven by a motor 20. Because of the inherent flexibility of the U-shaped insert 9, resulting both from its cross-sectional form and from its reduced wall thickness, particularly at the outermost portion 9, no serious stresses arise either by reason of the high heat transfer or by the unequal expansions of the inner and outer parts of the casting l. The cooling agent ultimately passes into a steam separator 2|, the unvaporized water being returned by conduit 22 to the pump IS. The water-driven pump 23 supplies feed water through the conduit 24 to the cooling system to replace that which is withdrawn in the form of steam by the conduit 25.

The invention is of great advantage also at the points where the difierent sections of the explosion chamber C are united. In prior constructions, very great accumulation of material occurred at these joints where the walls of the adjacent sections abutted against each other. By the construction in accordance with the invention, a greatly reduced amount of material is located at the joints 26 where only the relatively thin walled corner inserts l5 abut.

By providing a region of minimum wall thickness at the central or median line of the inserts, as indicated at 8 and I1, a still greater flexibility or resiliency is imparted to the inserts. Preferably, and as already indicated, the thickness of the insert wall tapers immediately from the region of union with the main casting to the central portion of minimum thickness; however, the legs of the inserts may, if desired, for a short distance from the line of juncture with the casting, be of substantially the same thickness as the wells of the casting, and thereafter fall gradually in width to the region of minimum width of wall.

Obviously, the features of invention hereinabove described in the constructional examples of Figs. 1 and 2 can correspondingly find application in other cast machine parts where in consequence of an especially high heat transfer care must be taken to provide for a reduction or elimination of heat and temperature stresses.

I claim:

1. Arrangement for reducing the temperature stresses at the edge and corner pieces in otherwise integrally cast, hollow machine parts which are subjected to high temperatures in use, comprising a separately formed edge or corner piece inserted in the casting and rigidly connected therewith, said piece following the shape of the casting and its wall being relatively thin at the edge or corner and increasing in thickness toward the areas of juncture with the casting.

2. Arrangement according to claim 1, wherein the insert is constructed as an annular angle member and is integrally united with the cast ing by welding, the vertex region of the angle constituting the edge or corner aforesaid.

3. Arrangement according to claim 1, wherein the insert is constructed as an annular angle member and is integrally united with the casting by welding, the legs of the angle member being approximately perpendicular to each other, the vertex region of the angle constituting the edge or corner aforesaid.

4. Arrangement according to claim 1, wherein the insert is constructed as an annular angle member and is integrally united with the casting by welding, the angle member being of U-shaped cross-section.

5. In combination with an outlet valve for the combustion gases from a combustion chamber, a cast housing for the valve, and a separately formed valve seat connected to the housing, said seat including a portion forming an edge or corner for the housing, the wall at said portion being of reduced thickness and the wall of the seat increasing in thickness toward the areas of juncture with the housing, whereby stresses in the valve seat caused by high temperatures are reduced.

6. A combustion chamber formed of a plurality of wall-forming sections united in abutting relation, said sections in the region of union being provided with inserts rigidly connected thereto, and forming the internal corner portions of the sections, the wall of the inserts being of reduced thickness at the corner and the thickness increasing toward the areas of juncture with the chamber sections.

'7. The combination set forth in claim 5, wherein the said portion has a minimum wall thickness at the central part thereof, whereby the flexibility of the said portion is increased.

8. A combustion chamber formed of a plurality of wall-forming sections united in abutting relation, said sections in the region of union being provided with inserts of reduced wall thickness compared to that of the chamber sections. the

inserts of adjoining sections being in juxtaposition.

HANS HOLZWARTH. 

